Young men who eat pizza, chips and burgers may end up with drastically lower sperm counts.
A study of almost 3,000 men, aged only 18 to 20, found those with a ‘Western diet’, including processed meat, pizza, sugary drinks and snacks, have worse quality than those who eat healthily.
Vegetarian men have higher sperm counts, as do those whose diets include fish and whole grains, making them more fertile.
Men’s diets have worsened over the past few decades, coinciding with a fall in the average sperm count of almost 60 per cent, which some experts have warned could lead to the extinction of the human race.
When couples struggle to have a baby, in a third of cases it is because of problems with sperm, which some men could reverse by improving their lifestyle.
Researchers led by scientists from the Harvard TH Chan School of Public Health compared the sperm counts of healthy young men eating western diets with those who were vegetarian and those who ate a ‘prudent’ diet high in fish, chicken and vegetables or a traditional Scandinavian diet including whole grains and dairy.
Men with a highly western diet produced 25.6 million fewer sperm than men whose diet was least like this.
A normal sperm count contains 39 million or more according to the World Health Organisation.
Dr Jorge Chavarro, who led the study from Harvard, said: ‘We are seeing lower sperm counts and a few men fall below the WHO lower reference limits. This is the largest study to have found this in young men.
‘You would be surprised to see how sensitive young men are to things that might affect sperm count, because it’s a perceived measure of masculinity.’Commenting on the findings, Allan Pacey, professor of andrology at the University of Sheffield, said: ‘This just shows the power of diet to the way that testicles function.
‘It’s almost certain that this is down to an effect that those with the better diets are taking more antioxidants.
‘With pizza, chips and red meat we know that the antioxidant stress goes up and that is bad for sperm.’
The findings, presented at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE), come from 2,935 men who took a compulsory medical exam to determine their fitness for military service.
Their diet was examined to see how ‘western’ it was, including foods such as pizza, chips, processed and red meat, snacks, sugary drinks and sweets.
Men with the most western diets had the lowest counts.
The best counts were seen in those following a highly ‘prudent’ diet, including fish, chicken, vegetables, fruit and water.
They had an average of 42.8 million more sperm than the men who followed this diet least.
The next best diet for sperm count was a vegetarian diet followed by the Scandinavian one.
Most previous research on diet and fertility has focused on older couples trying to get pregnant, rather than showing effects on the sperm of healthy young men.
Professor Pacey said: ‘The fact you are seeing a group of young men who aren’t trying to conceive is quite powerful.
‘The concern would be, is it that poor diet younger in life will make a change that sticks with you?’